Method of forming a composite bronze gear ring



Nov. 10, 1964 J. F. KLEMENT 3,156,539"

METHOD OF FORMING A COMPOSITE BRONZE GEAR RING Filed April 27. 1961 INVFJV TOR. JohnEKlemenz flndrus Star/(e United States Patent 3,156,589 METHOD OF FORMING A COMPOSITE BRONZE GEAR RING John F. Klement, Milwaukee, Wis, assignor to Ampco Metal, Inc., Milwaukee, Wis., a corporation of Wisconsin Filed Apr. 27, 1961, Ser. No. 106,030 3 Claims. (Cl. 148-3) This invention relates to a gear ring and more particularly to a bronze gear ring centrifugally cast from two separate alloys and to a method of making the same.

Bronze gear rings are frequently used in a worm drive along with a hardened steel worm. The bronze gears are particularly suitable under conditions of variable loads and where the drive is operated for long periods of time, for the bronze gear will not overheat and requires a minimum of lubrication.

The present invention is directed to a centrifugally cast gear ring having an outer annular section containing the teeth and formed of a tin bronze, and having an inner section formed of a copper base alloy having a high coefficient of thermal conductivity. The outer section of the gear ring is formed of a tin bronze containing 9% to 14% tin and this alloy, which contains the gear teeth, has a low coefiicient of friction and a favorable proportional limit which enables the alloy to conform to the worm. In addition, the tin bronze alloy has high strength and has a uniform distribution of the copper-tin phase so that the alloy has good wear resistance.

The inner portion of the gear ring is formed of a copper base alloy having a high coefiicient of thermal conductivity so that the heat will be dissipated from the gear surface and thus prevent galling on the gear teeth.

In casting the gear ring of the invention the tin bronze alloy is cast centrifugally to form the outer section. Subsequently, the copper base alloy is poured into the rotating mold and cast centrifugally against the previously formed but still molten outer section to provide the composite gear ring.

In order to provide the necessary physical properties for the gear ring, after casting the composite ring is chilled to a temperature in the range of 700 F. to 1100 F. by an air blast or water spray. The gear ring is subsequently cooled to room temperature at a rate slower than 500 F. per minute. This initial cooling rate is necessary to provide a proper chill for the outer section as it is desired to have a chilled surface for the gear teeth.

In the composite bronze gear ring of the invention, the inner section of the ring has a substantially higher coeflicient of thermal conductivity than the outer section and this serves to increase the rate of heat transfer from the gear teeth, thereby increasing the overall performance of the gear teeth by providing better strength, anti-galling characteristics and better wear resistance with a lower coefiicient of friction.

Other objects and advantages will appear in the course of the following description.

The drawings illustrate the best mode presently contemplated of carrying out the invention.

In the drawings:

FIGURE 1 is a plan view of the gear ring of the invention; and

FIG. 2 is a transverse section taken along line 2-2 of FIGURE 1.

The drawings illustrate a gear ring 1 which is adapted to be attached to a central hub, not shown. The inner peripheral portion of the gear ring is provided with a tongue 2 adapted to be received within a recess in the hub and is secured therein by a series of bolts which extend through holes 3 in the tongue.

The outer peripheral surface of the gear ring is pro- 3,156,589 Patented Nov. 10, 1964 vided with a series of teeth 4 adapted to engage a worm or the like. The gear ring of the invention is a composite structure having an outer section 5 formed of a high strength tin bronze and an inner section 6 formed of a copper base alloy having a high rate of thermal conductivity.

The outer section 5 of the ring contains from 9% to 14% tin, 0.01 to 3.5% nickel and the balance copper. In addition, the tin bronze alloy may contain up to 5% of other alloying metals such as zinc and lead, and up to 1% phosphorus, zirconium and the like.

The following alloys are specific examples in weight percent of the tin bronze which may be empoyed as the outer section 5 of the gear ring:

The tin bronze used as the outer section of the gear ring has a low coefficient of friction and has a favorable proportional limit, not being too stiff, so that it will conform to the worm which is engaged by the teeth 4. In addition, the tin bronze has a tensile strength in the range of 38,000 to 65,000 p.s.i., a Brinell hardness under a 500 kg. load of to 130, and has a uniform fine distribution of the copper-tin phase so that the alloy has excellent Wear resistance. The tin bronze alloy gear section has a coefiicient of friction against a hardened steel worm under lubricated conditions using an extreme pressure lubricant, and with both the gear section and the worm having mating surfaces smoother than a 20 micro inch finish, of less than 0.090. For example, an alloy containing 11.0% tin, 1.5% nickel, 0.10% phosphorus and the balance copper has a tensile strength of 55,000 p.s.i. and a Brinell hardness under a 500 kg. load of about 100.

The copper base alloy to be used as the inner section 8 contains 60% to 97% copper and may contain up to 5% tin, up to 10% lead, up to 10% aluminum, up to 30% zinc, up to 10% nickel, up to 5% silicon and up to 5% manganese. Specific examples of the copper base alloy which may be used as the inner section 8 are as follows in weight percent:

The copper base alloy used as the inner section 8 should have a coefficient of thermal conductivity greater than 22 B.t.u./sq. ft./hr./ F. and preferably the coeflicient of thermal conductivity will be in the range of 70 to Btu/sq. ft./ft./hr./ F. With this high coefiicient of thermal conductivity, heat will be quickly dissipated from the gear surface so that galling will be prevented. In addition, the copper base alloy inner section has a shear strength equivalent to that of the alloy of the outer section and generally in the range of 30,000 to 50,000 p.s.i., has a hardness in the range of 50 to Brinell under a 500 kg. load.

The gear ring of the invention is formed by centrifugal casting. In the casting method, the rotating mold may be formed of sand, graphite, cast iron, refractory materials, or the like, and it is preferred to initially heat the mold to a temperature in the range of 100 to 1000 F. before pouring to eliminate the moisture in the mold surface and also to prevent lapping of the molten alloy as it is poured into the mold. The temperature of the mold is predetermined for each design of casting and particular alloy used.

The tin bronze which composes the outer section is initially poured into the rotating mold at a temperature generally of about 2150 F. After pouring, the tin bronze is cooled to a temperature in the range of 1800 to 1900 F., while continually rotating the mold, and the copper base alloy is then poured into the mold. If the temperature of the tin bronze outer section is below 1800 F. when pouring the copper base inner section, the inner section will form laps, while if the tin bronze is at a temperature above 1900 F., dilution will occur between the two alloys.

The molten copper base alloy which is poured into the rotating mold fuses to the previously poured tin bronze alloy to form a joint which resembles a weld.

To provide the necessary physical properties for the composite gear ring, a cooling procedure is used after the alloys have been cast. In this procedure the composite gear ring is initially chilled to a temperature in the range of 700 F. to 1100 F. and preferably about 900 F. at a rate faster than 200 F. per minute per inch of section thickness such as by an air blast or water spray. After this initial cooling period the alloy is then cooled to room temperature at a rate slower than 500 F. per minute per inch of section thickness.

The thickness of the outer section 5 with respect to the inner section 6 depends upon the specific alloys used, the tooth construction, the particular application for the gear ring and the like. Generally, the thickness of the outer section will be from 30% to 70% of the overall thickness of the gear ring.

While the above description is directed to the outer section 5 containing the teeth 4, it is contemplated that in certain situations, such as a screw down nut for steel mill operation, the inner annular section will contain the teeth. In the situation where the teeth are on the inner section of the gear ring, the inner section would then be composed of the tin bronze and the outer section would be formed of the high thermal conductivity copper base alloy.

The gear ring of the invention includes an annular sec- 4: tion having high strength and wear resistance making it particularly suitable for a gear, and a second annular section bonded to the first and having a high rate of thermal conductivity, thereby increasing the rate of heat dissipation and preventing galling on the gear surface.

Various modes of carrying out the invention are contemplated as being Within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. A method of forming a composite bronze gear ring, comprising the steps of pouring a molten tin bronze alloy containing from 9% to 14% tin into a rotating mold to centrifugally cast an outer section of the gear ring, cooling the outer section to a temperature in the range of 1800 F. to 1900 F. while rotating the mold, pouring a molten copper base alloy into the mold while rotating the same to centrifugally cast the copper base alloy against the inner surface of the outer section to form an inner section of the gear ring, said copper base alloy having a coefiicient of thermal conductivity greater than 22 B.t.u./sq. ft./ft./hr./ F. and being bonded to the first section to provide a composite bronze gear ring, cooling the composite gear ring to a temperature in the range of 700 F. to 1100 F. at a rate faster than 200 F. per minute per inch of section thickness, and cooling the gear ring from said temperature in the range of 700 F. to 1100 F. to room temperature at a rate slower than 500 F. per minute per inch of section thickness to provide a chilled surface for the outer section of the gear ring.

2. The method of claim 1 in which the copper base alloy has a coefficient of thermal conductivity in the range of to B.t.u./sq. ft./ft./hr./ F.

3. The method of claim 1 in which the tin bronze alloy contains from 0.01 to 3.5% nickel.

References Cited in the file of this patent UNITED STATES PATENTS 464,165 Raymond Dec. 1, 1891 1,212,608 Calkins Jan. 16, 1917 2,042,800 Pike June 2, 1936 2,681,485 Smith June 22, 1954 2,710,997 Krepps June 21, 1955 3,094,753 Klernent June 25, 1963 OTHER REFERENCES Cast Bronze, by Harold J. Roast. Published by the A.S.M., 1953, pages 1724 relied on. 

1. A METHOD OF FORMING A COMPOSITE BRONZE GEAR RING, COMPRISING THE STEPS OF POURING A MOLTEN TIN BRONZE ALLOY CONTAINING FROM 9% TO 14% TIN INTO A ROTATING MOLD TO CENTRIFUGALLY CAST AN OUTER SECTION OF THE GEAR RING, COOLING THE OUTER SECTION TO A TEMPERATURE IN THE RANGE OF 1800*F. TO 1900*F. WHILE ROTATING THE MOLD, POURING A MOLTEN COPPER BASE ALLOY INTO THE MOLD WHILE ROTATING THE SAME TO CENTRIFUGALLY CAST THE COPPER BASE ALLOY AGAINST THE INNER SURFACE OF THE OUTER SECTION TO FORM AN INNER SECTION OF THE GEAR RING, SAID COPPER BASE ALLOY HAVING A COEFFICIENT OF THERMAL CONDUCTIVITY GREATER THAN 22 B.T.U./SQ. FT./FT./HR./*F. AND BEING BONDED TO THE FIRST SECTION TO PROVIDE A COMPOSITE BRONZE GEAR RING, COOLING THE COMPOSITE GEAR RING TO A TEMPERATURE IN THE RANGE OF 700*F. TO 1100*F. AT A RATE FASTER THAN 200* F. PER MINUTE PER INCH OF SECTION THICKNESS, AND COOLING THE GEAR RING FROM SAID TEMPERATURE IN THE RANGE OF 700* F. TO 1100*F. TO ROOM TEMPERATURE AT A RATE SLOWER THAN 500*F. PER MINUTE PER INCH OF SECTION THICKNESS TO PROVIDE A CHILLED SURFACE FOR THE OUTER SECTION OF THE GEAR RING. 